<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
  <style>
      /**/
    h2{color: blue}
  </style>
    <link rel="stylesheet" href="my.css">
</head>
<body>
<!--内联样式-->
<h1 style="color: red">内联样式1</h1>
<h1 style="color: red">内联样式2</h1>
<h2>内部样式1</h2>
<h2>内部样式2</h2>
<h3>外部样式1</h3>
<h3>外部样式2</h3>

</body>
</html>